Electrode array system for measuring electrophysiological signals

ABSTRACT

An array of electrodes is constructed to allow the user to easily adjust to the correct size of the patient&#39;s head. The array is self-adhesive, pre-gelled and disposable. The array fits easily over the temple and forehead areas where EEG signals can be acquired by specially designed monitors for purposes of monitoring a number of bodily phenomena, including but not limited to, depth of anesthesia, and/or ischemia, and burst suppression. The array is connected to the monitor via a tab connector that is integral to the disposable device. The tab connector is insertible into a reusable connector that is part of a monitoring system.

BACKGROUND OF THE INVENTION

This invention relates to physiological electrical signal monitors andmore particularly to a self-prepping multiple electrode array to connectto such monitors.

Surgical procedures are becoming more non-invasive, and as a result theuse of non-invasive electrophysiological monitoring to evaluate globalchanges of a patient's condition during surgical procedures hasincreased significantly. For example, EEG monitors are now being usedfor monitoring cerebral function during intra-operative procedures. Ofparticular interest are the assessment of the effects, of anesthetics,the evaluation of asymmetric activity between the left and righthemispheres of the brain in order to detect cerebral ischemia, and thedetection of burst suppression.

One of the greatest impediments to making intra-operative EEG monitoringmore widely practiced in the medical community is the traditional use ofmultiple electrodes in the standard International (10-20) ElectrodePlacement on the head, primarily in the scalp. Applying them takesconsiderable time and expertise, requires multiple, separate and timeconsuming skin preparation steps, and leaves the patient's scalp andhair in disarray.

Various headsets and caps are studded with different style electrodes tospeed this process, but such headsets and caps are generally notdisposable (and therefore must be cleaned), need to be adjusted toaccommodate the widely varying dimensions of the patients' heads, andrequire a considerable up-front cost. Other problems are encountered inthe present medical environment when such headsets and caps are designedto be single-use disposable devices because such devices are on occasionre-used despite warnings, which results in the spread of infection. Suchheadsets and caps have also been used with equipment for which it wasnot designed, which may be a well intentioned cost saving practice, butwhich could result in degraded performance of the device.

The most widely used electrodes are the reusable "gold cup" styleelectrodes that are small, bare tin, silver, or gold plated metal cupson the end of unshielded wires that may be several feet long. Suchelectrodes may require that the multiple scalp and forehead electrodesites first be located by measuring and marking the head. Such sitesmust then be prepared before applying the electrode in order to get goodelectrical contact. This preparation is usually accomplished by abradingthe electrode sites with a grit-impregnated solution or with some otherabrasive means to remove the outer layers of skin which cause the poorelectrical contact. The electrodes, up to 19 on the scalp for the fullInternational (10-20) electrode placement, are then individually appliedwith adhesive to the prepared sites in contact with a blood-enrichedskin layer, and are then injected with conductive electrolyte creamthrough the hole in the top of the electrode, thereby providing arelatively low electrical contact impedance. This process leaves thepatient with abraded spots, adhesive, and electrolyte cream throughoutthe scalp. Frequently, contact between the metal electrode and the skinoccurs, causing a time-varying offset voltage that results in "baselinewander." The electrodes also need to be placed with reasonable accuracyto achieve the standard placements or montages and to be able to repeatthe same measurement at a later time.

The need to use multiple, separate preparation steps makes the set-up avery time consuming process, taking perhaps up to half an hour of amedical technician's time for even a small subset of the fullInternational (10-20) Electrode Placement. The amount of expertise andtime required to prepare a patient is presently an impediment tointraoperative EEG monitoring being more widely practiced. Also, care isneeded to bundle the unshielded leads to reduce electrical noiseinterference. Additionally, after the procedure is over, the gold cupelectrodes and any placement harness need to be cleaned and sterilizedsince they are not intended to be disposable.

A number of prior art multiple electrode assemblies have been developedfor EEG monitoring. U.S. Pat. No. 4,595,013 issued to Jones; U.S. Pat.No. 4,928,696 issued to Henderson; U.S. Pat. No. 4,638,807 issued toRyder; U.S. Pat. No. 4,072,145 issued to Silva; and U.S. Pat. No.3,490,439 issued to Rolston are several examples. These multipleelectrode assemblies, however, all require some or all of the multiple,separate and time consuming steps of skin preparation described above toreduce the contact impedance with the skin before they are applied tothe body. These separate skin preparation steps also make it difficultto improve contact impedance once the electrode has been applied to thepatient or after the medical procedure is underway. If the preparationwas inadequate at the time the multiple electrode assembly is applied,it must be removed, the skin reabraded, and most likely a new electrodeassembly would have to be reapplied, adding additional expense to theadditional preparation time. Too much abrasion can cause a skin injury,or bleeding, leaving the patient with a lasting wound. Separate devicesrequired to abrade the skin cause the risk to the applicator bypotential contact with blood and by possible disease transmittal duringpreparation.

There are also a number of prior art multiple electrode assemblies thatare self prepping. U.S. Pat. No. 4,709,702 and associated electrode U.S.Pat. No. 4,640,290, both issued to Sherwin, utilize an array of springloaded metal "tulip" electrodes in a reusable headset that penetratesthe outer dead layers of skin to achieve a low contact impedance. Also,U.S. Pat. No. 4,770,180 and associated electrode U.S. Pat. No. 4,706,679both issued to Schmidt utilize an array of stiff, bundled metal wiresthat contact and penetrate the patient's skin. The drawback with both ofthese assemblies is that the metal contact with the skin causes highlyundesirable time-varying offset voltages that interfere with thesensitive measurement of the small signal voltages of the body. Also,both of these assemblies, and other assemblies that utilize a headset orcap such as the assembly described in U.S. Pat. No. 4,967,038 issued toGevins, need some adjustment to properly position the electrodes on thewidely varying dimensions of the patients' heads, and require a highup-front cost and cleaning after use.

U.S. Pat. No. 4,936,306 issued to Doty utilizes a spiral coil electrodethat may be metallic, and that uses cork-screws into patient's skin toachieve low contact impedance. While this may achieve low contactimpedance, it has the significant drawbacks of discomfort to the patientand creating sites of possible infection because of the deep skinpunctures made by the spiral coils. If made of metal, the spiral coilswill also cause time-varying voltages. Lastly, these electrodes areactually applied individually since they must be screwed into thepatient's scalp, which adds time to the procedure.

U.S. Pat. No. 4,683,892 issued to Johansson utilizes a headset withmultiple electrodes that are activated by compressed air, which impingeagainst the patient's scalp, and that also dispense electrolyte paste toimprove contact. This is a complex and expensive device, not intendedfor general, routine use in an intraoperative environment.

It is therefore a principal object of the present invention to provide adisposable, pre-gelled, self-prepping multiple electrode array whicheasily and reliably prepares the skin to assume a relatively low contactimpedance.

Another object of the present invention is to provide a self-preppingmultiple electrode array that does not require the use of more than onecomponent to be handled by the person applying the device, and fits mosthead sizes in the general patient population.

Still another object of the present invention is to provide a multipleelectrode array that can monitor cerebral function without the use ofelectrodes placed in the scalp, and that is easily aligned on the head.

A further object of the present invention is to provide a multipleelectrode array that prevents its use with monitoring equipment withwhich it was not intended to be used.

SUMMARY OF THE INVENTION

An array of electrodes is constructed to allow the user to easily adjustto the correct size of the patient's head. The array is self-adhesive,pre-gelled and disposable. The array fits easily over the temple andforehead areas where EEG signals can be acquired by specially designedmonitors for purposes of monitoring a number of bodily phenomena,including but not limited to, depth of anesthesia, and/or ischemia, andburst suppression. The array is connected to the monitor via a tabconnector that is integral to the disposable device. The tab connectoris insertible into a reusable connector that is part of a monitoringsystem.

The reusable connector is made of rigid contacts positioned side by sidewithin a keyed cavity. The contacts press against conductors of thedisposable array when the conductors are inserted into the cavity of thereusable connector. The conductors of the disposable array are laid on aflexible circuit constructed of a polyester substrate that has a plasticclip as its backing and support. The flexible circuit when routedthrough this clip forms the tab connector. This sensor tab connector,when inserted into the reusable connector cavity, electrically connectsthe electrodes to the monitor, allowing the acquisition of theelectrophysiological signals. The clip of the tab connector is selfsecuring, and thus does not need any additional securing mechanism tokeep the flexible circuit in place. The reusable connector and thedisposable connector have complementary locking mechanisms that providefor a secure connection.

Depending on the application and uniqueness of the array, a tabconnector may be used which includes a key that only fits to specificmonitors. The array also can communicate with the monitor to indicatethe type of application utilizing the electrodes and how many channelsneed to be configured.

The array contains two or more elements that when pressed against theskin lower their contact impedance to the skin and thus provide betterquality signals. The elements contain built in blowout pockets thatallow for the gel to adjust itself when pressure is applied to it. Suchpockets also prevent the gel from getting blown into the adhesive areasor running into other element areas, which could cause channels to shortcircuit.

These and other objects and features of the present invention will bemore fully understood from the following detailed description whichshould be read in conjunction with the accompanying drawings in whichcorrespondence reference numerals refer to corresponding partsthroughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the preferred embodiment of theelectrode array of the present invention;

FIG. 2 is a side sectional view of the electrode array shown in FIG. 3taken along lines 2--2 of FIG. 3;

FIG. 3 is a top plan view of the electrode array shown in FIG. 1;

FIG. 4 is a bottom sectional view of the electrode array shown in FIG.2;

FIG. 5(a) through 5(c) are perspective views of a tab clip assemblyutilized by the electrode array shown in FIG. 1 with a substrate isrouted through it;

FIGS. 6(a) and 6(b) are top plan views of the EEG connector system usedwith the electrode array shown in FIG. 1 with FIG. 6(a) showing theconnectors engaged and FIG. 6(b) showing the connectors disengaged;

FIGS. 7(a) through 7(e) are elevational views of keys used in the EEGconnector system shown in FIGS. 6(a) and 6(b);

FIG. 8 is a schematic diagram of the configuration coding utilized bythe EEG connector system shown in FIGS. 6(a) and 6(b) in its presentconfiguration;

FIG. 9 is a flowchart of the steps taken to identify an electrode arraytype.

FIG. 10 is a bottom plan view of the electrode array shown in FIG. 1;

FIG. 11 is a diagram showing locations on the head where electrodes arepositioned for 2 channel monitoring;

FIG. 12 is a perspective view of the gel blowout pockets and salt bridgebarriers utilized by the electrode array shown in FIG. 1;

FIGS. 13(a) and 13(b) are representations of a human head showing thelocations of the placement of electrodes for one channel monitoring;

FIG. 14 is an elevational view showing the sponge over tinesconstruction of the electrodes of the present invention;

FIG. 15(a) is a top plan view of an alternate embodiment the electrodearray of the present invention which includes two elements for templeconnection;

FIG. 15(b) is a bottom plan view of the electrode array shown in FIG.15(a);

FIG. 16 is a representation of a human head with an alternate embodimentof the electrode array locating the connector in an alternate location,being placed thereon;

FIG. 17 is another representation of a human head on which anotheralternate embodiment of the electrode array of the present invention ispositioned; using the mastoid locations to place the two satelliteelectrodes.

FIG. 18 is a side plan view of a female portion of an alternateembodiment of the connector used in the present invention and a top planview of the connector;

FIG. 19 is a plan view of the components of a system utilizing theelectrode array shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1-4, an electrode array 10 is shown. In a preferredembodiment the array 10 includes three electrodes 12 that are selfadherent and self prepping to the forehead and temple areas and that areused to acquire electrophysiological(EEG) signals. This array 10comprises a flexible circuit 14 containing silver/silver-chloride(Ag/AgCl) conductors 16 on a polyester substrate. These conductors arerouted from specific montage locations to a single connecting tab 18.There can be up to eight (8) conductors 16 for providing up to eightsignal lines of EEG data which can be captured simultaneously. This tab18 contains a clip 20 which adds rigidity, a locking mechanism, selfalignment, polarity and a keying mechanism to the array. The clip 20also adds a solid contact area to the flexible circuit 14.

The array 10 comprises a main body 14 which in the embodiment shownincludes two electrodes 12a, 12b and a satellite body 15 which includesone electrode 12c. The satellite body 15 allows the monitoring personnelto adjust the placement of the electrode 12c mounted on the satellitebody 15 due to the patient's head size. Extension 17, through whichconductors 16 run, connects the main body 14 to the satellite body 15.

Referring to FIGS. 3 and 14, each of the three electrodes 12 mounted inthe array 10 contain a self prepping disk 30 which includes a set offlexible tines 44 mounted with adhesive 45. The flexible tines 44extended beyond the surface of the gel 40 to contact the skin 32 as partof the normal application of the electrode 12 to the skin 32. Whenpressure is applied to the electrodes 12, the flexible tines 44 arepushed through foam layer 42 against the skin 32, which causes the tines44 to part the high impedance outer layers of skin 32 to expose the lowimpedance, blood-enriched layers without scratching or abrading. Thisprepping disk is made out of a plastic such as nylon constructed ashooks from hook and loop fasteners of the type often said under theVelcro trademark. These hooks are then sheared to the correct height andstiffness. The electrodes 12 are surrounded by an adhesive backed foamlayer 43. The array contains markers 13 that indicate the correctlocations that need to be pressed to achieve the desired skin impedance.

Referring to FIGS. 4 and 12, the array contains two blowout pockets 38,built into the basepad 39, that allow the gel 40 to adjust its volumeover a large area and prevent it from migrating to areas where it couldcause malfunction, such as short circuiting the two elements adjacent toone another.

The blowout pockets 38 are formed by cutting cylindrical shapes into thebasepad 39 foam material. In addition to the blowout pockets 38, thearray 10 also contains two salt bridge barriers 46 which preventelectrolyte gel 40 from one electrode from contacting the gel 40 of theother electrode which could cause the signals to short circuit. Thebarriers 46 are also cut into the adhesive basepad 39.

In the preferred embodiment a liquid hydrogel is used that rests on thegel pockets 38 cut within the basepad material 39. The gel 40 isretained within the pocket by a polyurethane foam sponge 42. The spongecontains large enough pores that allow the tines 44 to go through thepores and contact the skin 32 during use. The tines 44 then work in thesame manner as described in U.S. Pat. No. 5,305,746 the teachings ofwhich are incorporated herein by reference.

In a number of embodiments, the array 10 is mounted over the foreheadwith its reference electrode 12b over the center of the forehead. Asshown in FIGS. 13(a) and 13(b), the ground electrode 12a is placed overthe forehead as well. The third electrode 12c in the satellite body 15is positioned over the temple area. In most cases, either the right orleft temple is acceptable. Such an array may also be used for EMGdetection in the facial area.

The tab connector of the present invention is shown in FIGS. 5(a)-5(c).In FIG. 5(a) the conductors 16 which are mounted on a flexible materialare inserted into the clip 20 past the edge 46 of the clip 20. The clip20 includes a hinge 47 which is folded back as shown in FIG. 5(b) untilit is rotated a full one hundred eighty degrees as shown in FIG. 5(c). Aslot 48 is provided on each side of clip 20 for locking with extension49 so that the clip 20 stays in a locked and closed position as shown inFIG. 5(c), so that it is ready to be used.

Referring to FIG. 10, the tab connector 18 of the array 10 of thepreferred embodiment has eight (8) conductors. Out of the eightconductors, three are EEG signal lines 16a, 16b, 16c, and four arelogical signal lines 16e, 16f, 16g, 16h used to identify the appropriatearray type being connected. In the embodiment shown, the eighthconductor 16d is not used. The unused conductor 16d could be used inother embodiments as an additional EEG signal line or as an additionalmeans to identify an array type. It is important that the sensor sendsthe identification information to the monitor, so that the monitor candetermine the number of active elements used as well as their locationson the head. This way a monitor will auto configure for a particular EEGmonitoring session.

The preferred embodiment uses a three bit binary code identificationscheme such as the identification scheme described in U.S. patentapplication Ser. No. 08/545,981, now U.S. Pat. No. 5,813,404, which isassigned to the assignee of the present invention and the teachings ofwhich are incorporated herein by reference. In such an identificationscheme, the code is hard-wired in the flexible circuit of the particulararray 10. A digital signal converter in the monitor detects the array IDsignals. As shown in FIG. 8, the code is set by selectively shorting acommon drive signal line [SEN₋₋ DRV] 60 to the three code signal lines[SEN₋₋ 0:21] 62, 64, 66. These are the three array identification signallines. The [SEN₋₋ DRV] line is pulsed (driven) to a logic high at 8,192Hz by the pulse generator located on a monitor's digital signalconverter. Pulsing the line prevents a fault condition, such as a brokenconnection, from injecting more than 50 micro amps of current into apatient, as required by medical equipment standards, such as IEC-601-1.

The frequency of the pulse is chosen to be at the Nyquist frequency ofthe digitizers. These pulses will not interfere with the EEG signalbecause at this frequency it will alias onto itself only in the firststage of decimation, and will subsequently be filtered out completely bythe digital signal processor.

The patient interface connector code signal lines are pulled down to alogic "0" by resistors 70, 72, 74 located in the digital signalconverter 146 at the input to the receiver circuit 76, which is aD-Flip-flop in a preferred embodiment. As the common [SEN₋₋ DRV] line 60is driven high by the pulse generator, the patient interface connectorcode lines [SEN₋₋ 0:2] 62, 64, 66 are then read (i.e. clocked in) byreceiver circuit 76, which transmits the binary code to the monitor 150.The patient interface connector code signal lines that are shorted tothe drive signal will be read as a logic "1." The patient interfaceconnector code signal lines that are left open will be read as a logic"0." Such a coding scheme allows for eight different PIC cable types asfollows:

    ______________________________________                                        #      Code     Cable Type                                                    ______________________________________                                        1      000      PIC not connected                                             2      001      2 channel Bipolar (5 signal wires in use)                     3      010      2 channel Referential (4 signal wires in use)                 4      011      1 channel electrode connection                                5      100      1 channel sensor connection                                   6,7,8           Unassigned Spares                                             ______________________________________                                    

Referring now to FIGS. 9 and 19 the process for determining theappropriate C will now be described. In step 82, a CPU in the monitor150 periodically reads PIC code, which in a preferred embodiment is readevery 1.75 seconds. In step the CPU in monitor 150 reads a PIC ID in themanner described above with reference to FIG. 8. If the PIC ID isdetermined in step 86 to be "000," (which indicates that a PIC is notconnected) the system reiterates the process after each 1.75 seconddelay and continues to attempt to read a new PIC ID.

If the PIC ID is determined in step 88 to be "010," a two channelreferential EEG electrode set is detected and the monitor 150 isconfigured for 2-channel referential EEG processing in step 90. Thedigital signal convertor is set to referential mode in step 92. If, instep 94, the PIC ID is equal to "010," the system recognizes a twochannel bipolar EEG electrode set and the monitor 150 is configured forthe appropriate EEG processing in step 96. The digital signal convertor146 is then set in step 98 to bipolar mode.

If the PIC ID is determined in step 100 to be equal to "011," the systemhas detected a one channel EEG processing cable and the monitor 150 isconfigured for 1-channel EEG processing in step 102. In step 106,digital signal converter is set to bipolar mode. If any other PIC ID isdetected, error messages are generated and displayed in step 107indicating that an illegal PIC ID was detected, and that no EEGprocessing should occur. After the CPU in monitor 150 determines thatthe PIC ID is valid, the monitor checks if the PIC ID is a new PIC ID.If a new PIC ID is recognized the monitor initiates a self test in step108 followed by an electrode impedance test in step 109. After thisseries of steps the system again returns after a 1.75 second delay toread additional PIC IDs in step 82.

In alternate embodiments where four pins are allocated for PIC IDs, thedigital signal convertor 146 can recognize up to 15 differentcombinations of pigtail, PIC or connector type.

The current connector system allows either a single channel electrodearray or a dual channel electrode array. As shown in FIGS. 7(a)-7(e), italso provides a keying safeguard that allows for the connector to beselective as to what can physically be plugged into it. By modifying theheight of the connector rails 50 one can allow for a specific array tobe a master key (FIG. 7(a)) and other arrays to be specific to a matingconnector. This keying mechanism can be used for example to physicallydifferentiate between array types. For instance, an array that allowssingle and dual channel monitoring, and one that allows only dualchannel monitoring. The master key is then available to connect to allmonitors indiscriminately. For instance, it can be used to insert a testcircuit to service the monitor, or used to insert a multipurpose array.

Referring to FIGS. 6(a) and 6(b), the tab connection on the array ha s alocking mechanism, including extension 120 and receptor region 122 thatsecures it to the reusable connector 124. The locking action providesthe user with tactile and audible feedback.

The reusable connector 124 includes a printed circuit board withcontacts and wires from a cable attached to it. The printed circuitboard is then inserted into an assembly of two pre-molded housings secured together by ultrasonic welding.

The electrode array 10 described above is used in connection with a newnon-standard electrode positioning (montage) for measuring the effectsof anesthetics on the brain as well as other cerebral phenomena.

Referring to FIGS. 13(a) and 13(b), one embodiment of this montage isshown in which the reference electrode 12 is placed in the center of theforehead with the satellite electrode 12 being placed on the temple ateye level above the ear. This montage has several advantages overpreviously described montages, as it makes it easy to locate theelectrodes on the patient, the electrodes are easy to apply to thepatient and the EEG signal and the amplitude of such signal aresufficient for the purposes for which they are used.

The location of the electrodes is important for monitoring the effectsof anesthetics. Prior art for monitoring the effects of anesthetics havedescribed EEG systems using from 2 to 19 EEG channels, where theelectrode locations have been identified by the international 10-20systems. The electrode arrays described above use 1 or 2 EEG channels.The specific electrode locations described in this patent are positionedin a unique anterior area of the subject's head from which EEG signalshave not traditionally been taken. These anterior placed arrays takeadvantage of the global nature of the effects of anesthetics on thebrain. That is to say that the global effects of anesthetics arereflected in the EEG detected near the anterior cerebral cortex. Theelectrode array described above provides a rather large EEG signalbecause of the inter-electrode spacing that has been selected. Theelectrodes, however, are not so widely spaced as to increase a noisesignal generated by the subject (e.g. EKG). In any signal processingsystem, increases in signal amplitude without an increase in the noiseamplitude is desirable. This is particularly true with EEG monitoringbecause EEG is on the order of one hundred times smaller than theelectrocardiogram (EKG). The electrode array 10 facilitates the locatingof the electrodes 12 at positions referenced to easily identifiedanatomical landmarks (i.e. center of the forehead, eye socket). Inaddition, the electrode locations are entirely out of the subject'shair. This allows for easy application of the electrodes without theneed to shave or otherwise part the subject's hair.

A system utilizing the electrode array of the present invention may beconfigured in one or two channel monitoring modes. For the two channelmode shown in FIGS. 15(a) and 15(b), one EEG channel measures from anelectrode location on the subject's forehead to the left of the lowertemple area, proximal to the left eye socket (malar bone). The secondEEG channel measures from the same forehead electrode to the right lowertemple area, proximal to the eye socket. A non-measurement groundelectrode is also placed on the patient's forehead. The two channelsystem has the advantages of signal redundancy (two channels of signalinstead of one channel) and improved signal to noise ratio. The onechannel configuration, an example of which is shown in FIG. 1, uses thecenter forehead electrode plus either the left or right electrodedescribed above plus the ground electrode. The one channel configurationhas the advantage of using less space on the subject's head therebymaking an operation on the head easier since there is a greater areaover which to maneuver. The one channel configuration being easier toapply because of the use of one less electrode.

Referring to FIGS. 15(a) and 15(b), an alternate embodiment of thepresent invention is shown in which the array 10 of electrodes 12includes two temple electrodes 12c that allow for depth of anesthesia,burst suppression, ischemia monitor, and EEG recordings as well as EMGdetection. When a two channel system is used, the signals could beaveraged together or the second channel could be used as a backup signalif the first channel signals are lost. The placement of the electrodeson a human head in such a two channel system is shown in FIG. 11.Referring to FIG. 10, in this configuration, conductor 16d is used toprovide the signal from the second temple.

Referring to FIG. 16, the samne array 10 described above in connectionwith FIG. 1 is used in a different manner with the center of the mainbody 14 of the array 10 being placed over the temples and the electrode12c on the satellite body 15 becomes the reference electrode. Thisconfiguration offers the advantage of keeping the cable away from theface of the patient.

As shown in FIG. 17, another array 10 of electrodes 12 is shown with aground connection 12a two frontal connections and two mastoidconnections that can be used for depth of anesthesia, burst suppression,ischemia monitoring, and EEG recordings as well as EMG detection. Aswith the embodiments shown in FIGS. 15(a) and 15(b), the configurationshown in FIG. 17 can be used to capture a hemisphere signal on each sideof the head in order to produce bipolar readings.

In alternate embodiments, an array of electrodes will contain otherpassive devices such as but not limited to resistors, capacitors, orjumpers, for purposes of generating a code for self configuration.

In another embodiment shown in FIG. 18, the array 10 of multipleelectrodes 12 comprises of a flexible circuit with conductors thatterminate on a tab connection that is double sided. The mating connector124 has contacts 125 on top and bottom. This allows an increase in thedensity of the circuit while keeping the size of the connector to asmall profile. It also allows for the separation of signals that are ofdigital nature from those of physioelectric nature. This reduces theamount of noise on the EEG signals.

Referring now to FIG. 19, the electrode array 10 is shown in use with anEEG monitor. The electrode array 10 is connected through connector 20 toa patient interface cable 142 which in turn is connected to a pigtailcable 144. The pigtail cable 144 is connected to a digital signalconverter 146 which in turn is connected to monitor 150 through monitorinterface cable 148. In another embodiment, the digital signal convertermay be embedded in the monitor thereby eliminating the need for cables144, 148 or the electrode array 10 could also be connected to cable 144thereby eliminating the need for cable 142.

While the foregoing invention has been described with reference to itspreferred embodiments, various alterations and modifications will occurto those skilled in the art. All such alterations and modifications areintended to fall within the scope of the appended claims.

What is claimed is:
 1. An array of electrodes, including only threeelectrodes, for monitoring physiological electrical signals, said arraycomprising:a flexible unitary body having a main portion, one satelliteportion, and a flexible portion located between said main portion andsaid one satellite portion; two electrodes of the three electrodes beingprinted on said main portion and a third electrode of the threeelectrodes being printed on said satellite portions; conductors printedon said flexible unitary body to carry signals from said electrodes. 2.The array of electrodes for monitoring physiological electrical signalsof claim 1 wherein said array further comprises a non-conductive clipinto which said conductors are inserted and locked.
 3. The array ofelectrodes for monitoring physiological electrical signals of claim 2wherein said non-conductive clip comprises:a non-conductive body intowhich said conductors are inserted, said body having a first end and asecond end; a hinge positioned between said first end and said secondend about which said second end is rotated to be positioned in closeproximity to said first end; a locking mechanism for locking said secondend adjacent said first end.
 4. The array of electrodes for monitoringphysiological electrical signals of claim 2 wherein said non-conductiveclip further comprises at least two rails for guiding said clip into areusable connector of a monitor, said rails being dimensioned uniquelyfor a particular application.
 5. The array of electrodes for monitoringphysiological electrical signals of claim 1 wherein said array furthercomprises an adhesive material on one surface of said flexible body. 6.The array of electrodes for monitoring physiological electrical signalsof claim 1 further comprising non-conductive tines positioned beneatheach electrode for separating layers of a patient's skin.
 7. The arrayof electrodes for monitoring physiological electrical signals of claim 6further comprising a sponge positioned adjacent each electrode, saidtines being integrated into said electrode and said tines passingthrough said sponge to contact a patient's skin.
 8. The array ofelectrodes for monitoring physiological electrical signals of claim 1wherein said conductors are Ag/AgCl conductors.
 9. The array ofelectrodes for monitoring physiological electrical signals of claim 1further comprising means for storing a unique code on said unitaryflexible body.
 10. An array of electrodes, including only threeelectrodes, for monitoring physiological electrical signals, said arraycomprising:a flexible unitary body having a main portion, one satelliteportion, and a flexible portion located between said main portion andsaid one satellite portion; two electrodes of the three electrodes beingpermanently affixed to said main portion and a third electrode of thethree electrodes being positioned on said satellite portion; a layer ofelectrolytic gel adjacent at least one electrode; a blow-out compartmentfor storing said electrolytic gel out of contact with gel from any otherelectrode.
 11. An array of electrodes, including only three electrodes,for monitoring physiological electrical signals, said array comprising:aflexible unitary body having a main portion, one satellite portion, anda flexible portion located between said main portion and said onesatellite portion; two electrodes of the three electrodes beingpermanently affixed to said main portion and a third electrode of thethree electrodes being positioned on said satellite portion; a saltbridge barrier for preventing electrolytic gel in contact with one ofsaid electrodes from contacting electrolytic gel in contact with asecond of said electrodes, said salt bridge barrier comprising wellsthrough adhesive foam secured to said flexible unitary body.
 12. Anarray of electrodes for monitoring physiological electrical signals,said array comprising:a flexible body; at least two electrodes affixedto said flexible body; means for storing on said flexible body a codeunique to the array.
 13. The array of electrodes for monitoringphysiological electrical signals of claim 12 wherein conductors arepositioned on said flexible body to carry signals from said electrodes.14. The array of electrodes for monitoring physiological electricalsignals of claim 13 wherein said array further comprises anon-conductive clip into which said conductors are inserted and locked.15. The array of electrodes for monitoring physiological electricalsignals of claim 14 wherein said comprises:a non-conductive body intowhich said conductors are inserted, said body having a first end and asecond end; a hinge positioned between said first end and said secondend about which said second end is rotated to be positioned in doseproximity to said first end; a locking mechanism for locking said secondend adjacent said first end.
 16. The array of electrodes for monitoringphysiological electrical signals of claim 14 wherein said clip furthercomprises at least two rails for guiding said clip into a reusableconnector of a monitor, said rails being dimensioned uniquely for aparticular application.
 17. The array of electrodes for monitoringphysiological electrical signals of claim 13 wherein said conductors areAg/AgCl conductors.
 18. The array of electrodes for monitoringphysiological electrical signals of claim 12 wherein said array furthercomprises an adhesive material on one surface of said flexible body. 19.The array of electrodes for monitoring physiological electrical signalsof claim 12 further comprising non-conductive tines positioned beneatheach electrode for separating layers of a patient's skin.
 20. The arrayof electrodes for monitoring physiological electrical signals of claim19 further comprising a sponge positioned adjacent each electrode, saidtines being integrated into said electrode and said tines passingthrough said sponge to contact a patient's skin.
 21. An array ofelectrodes for monitoring physiological electrical signals, said arraycomprising:a flexible body; at least two electrodes affixed to saidflexible body; means for storing on said flexible body a code unique tothe array; a layer of electrolytic gel adjacent at least one electrode;a blowout compartment for storing said electrolytic gel out of contactwith gel from any other electrode.
 22. An array of electrodes formonitoring physiological electrical signals, said array comprising:aflexible body; at least two electrodes affixed to said flexible body;means for storing on said flexible body a code unique to the array; asalt bridge barrier for preventing electrolytic gel in contact with oneof said electrodes from contacting electrolytic gel in contact with asecond of said electrodes, said salt bridge barrier comprising wellsthrough adhesive foam secured to said flexible body.